drm/dp_mst: Add drm_dp_mst_aux_for_parent()

Add a function to get the AUX device of the parent of an MST port, used
by a follow-up i915 patch in the patchset.

v2: Move drm_dp_mst_aux_for_parent() forward declaration to this patch
    (Ankit)

Cc: Lyude Paul <[email protected]>
Cc: [email protected]
Reviewed-by: Ankit Nautiyal <[email protected]>
Acked-by: Maarten Lankhorst <[email protected]>
Signed-off-by: Imre Deak <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 46b99d5fe008..3577786b5db2 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -6011,6 +6011,22 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
 }
 
 /**
+ * drm_dp_mst_aux_for_parent() - Get the AUX device for an MST port's parent
+ * @port: MST port whose parent's AUX device is returned
+ *
+ * Return the AUX device for @port's parent or NULL if port's parent is the
+ * root port.
+ */
+struct drm_dp_aux *drm_dp_mst_aux_for_parent(struct drm_dp_mst_port *port)
+{
+	if (!port->parent || !port->parent->port_parent)
+		return NULL;
+
+	return &port->parent->port_parent->aux;
+}
+EXPORT_SYMBOL(drm_dp_mst_aux_for_parent);
+
+/**
  * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
  * @port: The port to check. A leaf of the MST tree with an attached display.
  *